acquirement through sexual selection of conspicuous colours, appears to
have been sometimes checked from the danger thus incurred. But in other
cases the males during long ages may have struggled together for the
possession of the females, and yet no effect will have been produced,
unless a larger number of offspring were left by the more successful
males to inherit their superiority, than by the less successful: and
this, as previously shewn, depends on many complex contingencies.
Sexual selection acts in a less rigorous manner than natural selection.
The latter produces its effects by the life or death at all ages of the
more or less successful individuals. Death, indeed, not rarely ensues
from the conflicts of rival males. But generally the less successful
male merely fails to obtain a female, or obtains a retarded and less
vigorous female later in the season, or, if polygamous, obtains fewer
females; so that they leave fewer, less vigorous, or no offspring. In
regard to structures acquired through ordinary or natural selection,
there is in most cases, as long as the conditions of life remain the
same, a limit to the amount of advantageous modification in relation to
certain special purposes; but in regard to structures adapted to make
one male victorious over another, either in fighting or in charming the
female, there is no definite limit to the amount of advantageous
modification; so that as long as the proper variations arise the work
of sexual selection will go on. This circumstance may partly account
for the frequent and extraordinary amount of variability presented by
secondary sexual characters. Nevertheless, natural selection will
determine that such characters shall not be acquired by the victorious
males, if they would be highly injurious, either by expending too much
of their vital powers, or by exposing them to any great danger. The
development, however, of certain structures of the horns, for instance,
in certain stags has been carried to a wonderful extreme; and in some
cases to an extreme which, as far as the general conditions of life are
concerned, must be slightly injurious to the male. From this fact we
learn that the advantages which favoured males derive from conquering
other males in battle or courtship, and thus leaving a numerous
progeny, are in the long run greater than those derived from rather
more perfect adaptation to their conditions of life. We shall further
see, and it could never have been anticipated, that the power to charm
the female has sometimes been more important than the power to conquer
other males in battle.
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